Spark plug insert



FIG. 1 side and top perspective view of a spark plug insert showing my new design;

FIG. 2 is a side and bottom perspective view thereof;

FIG. 3 is a top plan view thereof;

FIG. 4 is a front elevational view thereof;

FIG. 5 is a right side elevational view thereof;

FIG. 6 is a left side elevational view thereof;

FIG. 7 is a rear elevational view thereof; and

FIG. 8 is a bottom view thereof; and,

FIG. 9 is a side elevational view thereof, shown with environment.

The broken lines are directed to environment; the broken lines form no part of the claimed design. 

CLAIM The ornamental design for a spark plug insert, as shown and described. 